对 android 中的“onBindViewHolder 的工作”感到困惑

Question

我是一名初学者，我正在开发一个 Android 项目。我正在创建一个公告选项卡，其中包含字段标题、描述、事件位置、事件时间。 The Idea is Admin 应用程序的管理员将发布一些公告，所有应用程序用户都将收到公告。

在某些情况下，事件字段的位置和时间字段为空。因此，我创建了两个 Cardview 来显示公告。一个有这些字段，另一个没有这两个字段。因此，每当管理员不输入这两个字段时，适配器应切换到第二张卡片视图并应显示在回收器视图上。但是 Recycler 只显示一个视图，即使 Time 和 location 字段不存在。

Snapshot of CardView with All Fields

Snapshot of CardView without Location and Time fields

OnBindViewHolder：

添加了一个布尔标志名称 flagdatelocation 以了解这两个字段是否为空。因此，如果这些字段为空，我将 flagdatelocation 设置为 false，将其传递给 onCreateViewHolder 以便决定选择要选择的卡片视图。我已将 flagdatelocation 声明为类中的全局变量，并使用 true 对其进行初始化。（非静态）

注意：如果我没有启动标志为真，我会得到一个空指针异常。

 boolean flagdateLocation=true;

 protected void onBindViewHolder(@NonNull AnnounceHolder holder, int position, @NonNull Announcements model) {
     holder.textViewTitle.setText(model.getTitle());
     holder.textViewDesc.setText(model.getDescription());
    Log.d(TAG, "onBindViewHolder: "+model.getLocation()+" "+model.getDate());
     if (model.getDate()!=null&&model.getLocation()!=null){
         flagdateLocation = true;
         holder.textViewLocation.setText(model.getLocation());
         holder.textViewDate.setText(model.getDate());

     }
     else{
         flagdateLocation = false;
     }

    Log.d(TAG, "onBindViewHolder: 2"+flagdateLocation);


    String creationDate="";
    Date date = model.getTimestamp();
    if (date != null) {
        DateFormat dateFormat = SimpleDateFormat.getDateInstance(DateFormat.FULL, Locale.US);
        creationDate = dateFormat.format(date);
        Log.d("TAG", creationDate);
    }
     holder.textViewTodayDate.setText(creationDate);

}

OnCreateViewHolder：

我添加了 if Condition 来检查 OnBindViewHolder 中声明的标志，具体取决于这些字段是否为 null，因此选择所需的 Cardview。

public AnnounceHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View V;
   if (flagdateLocation == false) {
       V = LayoutInflater.from(parent.getContext()).inflate(R.layout.announcements_card_view_without_l_s, parent, false);
   }
   else{
       V = LayoutInflater.from(parent.getContext()).inflate(R.layout.announcements_card_view, parent, false);
    }


    return new AnnounceHolder(V);
}

Firebase 结构：

Cloud Firestore where the fields are updated depending on the Admin Announcing

问题是即使字段为空，Recyclerview 始终显示相同的 Cardview。 if 条件不知何故不起作用。我的问题是我的要求方法是正确的，或者需要实施任何其他方式。我哪里错了？

RecylerAdapter 总数：

public class AnnouncementsAdapter extends FirestoreRecyclerAdapter<Announcements, AnnouncementsAdapter.AnnounceHolder> {

boolean flagdateLocation;

public AnnouncementsAdapter(@NonNull FirestoreRecyclerOptions<Announcements> options) {
    super(options);
}

@Override
protected void onBindViewHolder(@NonNull AnnounceHolder holder, int position, @NonNull Announcements model) {
     holder.textViewTitle.setText(model.getTitle());
     holder.textViewDesc.setText(model.getDescription());
    Log.d(TAG, "onBindViewHolder: "+model.getLocation()+" "+model.getDate());
     if (model.getDate()!=null&&model.getLocation()!=null){
         flagdateLocation = true;
         holder.textViewLocation.setText(model.getLocation());
         holder.textViewDate.setText(model.getDate());

     }
     else{
         flagdateLocation = false;
     }

    Log.d(TAG, "onBindViewHolder: 2"+flagdateLocation);


    String creationDate="";
    Date date = model.getTimestamp();
    if (date != null) {
        DateFormat dateFormat = SimpleDateFormat.getDateInstance(DateFormat.FULL, Locale.US);
        creationDate = dateFormat.format(date);
        Log.d("TAG", creationDate);
    }
     holder.textViewTodayDate.setText(creationDate);

}

@NonNull
@Override
public AnnounceHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View V;
   if (flagdateLocation == false) {
       V = LayoutInflater.from(parent.getContext()).inflate(R.layout.announcements_card_view_without_l_s, parent, false);
   }
   else{
      V = LayoutInflater.from(parent.getContext()).inflate(R.layout.announcements_card_view, parent, false);
    }

    V = LayoutInflater.from(parent.getContext()).inflate(R.layout.announcements_card_view, parent, false);


    return new AnnounceHolder(V);
}


class AnnounceHolder extends RecyclerView.ViewHolder{
    TextView textViewTitle;
    TextView textViewDesc;
    TextView textViewLocation;
    TextView textViewDate;
    TextView textViewTodayDate;
    public AnnounceHolder(@NonNull View itemView) {
        super(itemView);
        textViewTitle = itemView.findViewById(R.id.title_announcements);
        textViewDesc = itemView.findViewById(R.id.description_announcements);
        textViewLocation = itemView.findViewById(R.id.location_announcemets);
        textViewDate = itemView.findViewById(R.id.date_announcements);
        textViewTodayDate = itemView.findViewById(R.id.todays_date);

    }
}

Answer 1

我希望这会有所帮助：

public AnnounceHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View V;

    V = LayoutInflater.from(parent.getContext()).inflate(R.layout.announcements_card_view, parent, false);

    return new AnnounceHolder(V);
}

还有：

protected void onBindViewHolder(@NonNull AnnounceHolder holder, int position, @NonNull Announcements model) {
 holder.textViewTitle.setText(model.getTitle());
 holder.textViewDesc.setText(model.getDescription());
Log.d(TAG, "onBindViewHolder: "+model.getLocation()+" "+model.getDate());
 if (model.getDate()!=null&&model.getLocation()!=null){
     
     //SET THE VIEWS YOU WANNA SEE TO VISIBLE
     holder.YOUR_DATE_FILED.setVisibility(View.VISIBLE);
     holder.YOUR_LOCATION_FILED.setVisibility(View.VISIBLE)

     holder.textViewLocation.setText(model.getLocation());
     holder.textViewDate.setText(model.getDate());

 }
 else{
     //SET THE VIEWS YOU DON'T WANNA SEE TO GONE
     holder.YOUR_DATE_FILED.setVisibility(View.GONE);
     holder.YOUR_LOCATION_FILED.setVisibility(View.GONE)
     
 }

Log.d(TAG, "onBindViewHolder: 2"+flagdateLocation);


String creationDate="";
Date date = model.getTimestamp();
if (date != null) {
    DateFormat dateFormat = SimpleDateFormat.getDateInstance(DateFormat.FULL, Locale.US);
    creationDate = dateFormat.format(date);
    Log.d("TAG", creationDate);
}
 holder.textViewTodayDate.setText(creationDate);

}